JOURNAL OF RAMAN SPECTROSCOPY J. Raman Spectrosc. 2007; 38: 483–495 Published online 3 December 2006 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/jrs.1670 Spectroscopic and computational studies on self-assembly complexes of bis(pyrrol-2- ylmethyleneamine) ligands linked by alkyl spacers with Cu(II) Wei Li, 1,2 Yibo Wang, 3 Lanying Yang, 4 Adriana Szeghalmi, 5 Yong Ye, 1 Jinshi Ma, 4 Mingdao Luo, 1 Ji-ming Hu 1,5 ∗ and Wolfgang Kiefer 5 1 College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, China 2 Department of Chemical Engineering, Wuhan University of Science and Engineering, Wuhan 430073, China 3 Department of Chemistry, Guizhou University, Guiyang, Guizhou 550025, China 4 CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China 5 Institut f ¨ ur Physikalische Chemie, Universit ¨ at W ¨ urzburg, Am Hubland, D-97074 W ¨ urzburg, Germany Received 20 June 2006; Accepted 21 September 2006 Bis(pyrrol-2-ylmethyleneamine) ligands and their mononuclear monomeric and dinuclear dimeric self- assembly complexes with Cu(II) were investigated by means of IR and Raman spectroscopies and density functional theory. The ground-state geometries were calculated by using the Becke–Lee–Yang–Parr composite exchange-correlation functional (B3LYP) and a combined basis set (LanL2DZ for Cu; 6–31G(d) for C, H, N), and they were compared with the single-crystal X-ray diffraction (XRD) structures. The DFT-calculated Cu – N bond lengths are generally higher by 0.001 – 0.040 ˚ A than those determined through XRD. The vibrational spectra were also calculated at the same level of theory for the optimized geometries. The calculated wavenumbers were scaled by a uniform scaling factor and compared with the experimental fundamentals. The predicted spectra are in good agreement with the experimental ones with the deviations generally less than 30 cm −1 . In comparison with the spectra of the ligands, the coordination effect shifts the u(C N) wavenumber by about 50 cm −1 toward a lower value. Because of the weak intermolecular C–H···Cu hydrogen bond, the Cu–N stretching mode is shifted toward a lower wavenumber. Copyright  2006 John Wiley & Sons, Ltd. KEYWORDS: bis(pyrrol-2-ylmethyleneamine); copper(II); vibrational spectra; density functional theory INTRODUCTION Metal-ion-assisted self assembly is one of most powerful approaches to supramolecular architectures. 1–4 During the past decade, there has been considerable interest in the con- struction of a plethora of metallosupramolecular species, such as coordination macrocycles, cages and coordination polymers. 5–13 In previous work, we used bis(pyrrol-2- ylmethyleneamine) Schiff bases bridged by flexible or rigid spacers for building distinct supramolecular complexes, such as coordination polymers, helicates and molecular triangle, square and network polymers. 14 – 20 Electrochem- ical methods to obtain metal complexes of such Schiff L Correspondence to: Ji-ming Hu, College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, People’s Republic of China. E-mail: jmhu@whu.edu.cn bases bridged by alkyl and aryl disulphide spacers have also been reported. 21 However, little information on the relationship between the structures of such complexes and their vibrational spectra is available because it is exceed- ingly difficult to develop accurate force fields for molecules of the size and complexity of CuL [L D bis(pyrrol-2- ylmethyleneamine)] on a purely empirical basis. Quantum mechanical calculations of force constants can solve the dif- ficulties of empirical force field determination by making independent information, which is largely complementary to the spectroscopic measurements. 22 As an economical and effective way of including electron correlation in the ground- state wave function, gradient-corrected density functional theory (DFT) is about as inexpensive as Hartree–Fock theory and is much more accurate for molecules com- posed of first-row atoms. Some previous studies have Copyright  2006 John Wiley & Sons, Ltd.